Solution deposition method for forming metal oxide or metal hydroxide layer

ABSTRACT

A solution deposition method includes: applying a liquid precursor solution to a substrate, the precursor solution including an oxide of a first metal, a hydroxide of the first metal, or a combination thereof, dissolved in an aqueous ammonia solution; evaporating the precursor solution to directly form a solid seed layer on the substrate, the seed layer including an oxide of the first metal, a hydroxide of the first metal, or a combination thereof, the seed layer being substantially free of organic compounds; and growing a bulk layer on the substrate, using the seed layer as a growth site or a nucleation site.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation of U.S. patent application Ser. No.14/537,487, filed on Nov. 10, 2014, now U.S. Pat. No. 9,702,054.

BACKGROUND

Field

Aspects of the present invention relate to a solution deposition methodfor forming a metal oxide or metal hydroxide layer.

Discussion of the Background

Metal oxide and metal hydroxide films are useful for a wide variety ofapplications and may be deposited by a number of different methods. Inmany of these cases, the deposition of a metal oxide or metal hydroxidefilm involves the use of a seed layer or nucleation layer, which isdeposited or processed under different conditions or by a differentmethod than the deposition of the bulk of the film. The purpose of aseed/nucleation layer may be to provide a uniform distribution anddensity of sites for additional material to be deposited during asubsequent growth process, and/or to create a different set ofproperties at the immediate interface with the substrate than those ofthe bulk of the film.

When synthesizing a new phase of matter on the surface of an existingphase, the new phase should nucleate before growing. Nucleation of a newphase has a higher energy barrier than continued growth of the newphase. As a result, some conditions that will result in growth on anexisting seed layer may not be adequate for nucleation on an unseededsubstrate of a different phase, and conditions necessary for nucleationon a substrate may lead to poor quality growth. Therefore, it is oftenbeneficial to split the formation of a film into separate nucleation andgrowth steps. This has been shown to be especially useful for the growthof metal oxides and metal hydroxides from solution.

Metal oxides and metal hydroxide films can be synthesized by a number ofsolution-based growth methods including, hydrothermal and solvo-thermalgrowth, chemical bath deposition (CBD), successive ionic layeradsorption and reaction (SILAR), Electroless Deposition, etc. Solutiongrowth methods have been used previously to synthesize a wide variety offilms and Micro/Nano-Structures. In many of these cases, the depositionof a uniform film or array of nano/microstructures involves the use of aseed (nucleation) layer.

A seed layer provides a uniform distribution of sites forlow-temperature solution growth. Without a seed layer, conditions usedfor solution deposition/growth typically lead to non-uniform and/or lowdensity distribution of nucleation sites, which develop into a lowdensity of spatially separated structures or “islands”, rather than adesired uniform array or film. Several different methods have previouslybeen explored for seed layer creation, including coating the substratewith a suspension of nanoparticles, coating with a metal-organicprecursor film, which, upon heating, decomposes and crystallizes into ametal oxide, vapor deposition of a thin metal oxide layer, and aqueousdeposition by initiating the rapid precipitation of a metal oxide fromsolution.

These techniques all have serious drawbacks, especially for thedeposition of epitaxial films. The use of nanoparticle seeds depositedfrom suspension is not compatible with epitaxy as it typically creates aseed layer with random orientation. The same is true for related artmetal-organic precursor film methods, unless very high temperatures areused to recrystallize the seed film. Vapor deposition is capable ofproducing epitaxial seed layers, but the use of such methods to producethe seed layer negates much of the potential cost or other processingadvantages of using low temperature aqueous solution deposition for thesubsequent bulk film growth.

Recently, thin films of ZnO and related materials have been demonstratedusing a solution process where a precursor solution is prepared by thedissolution of zinc oxide or zinc hydroxide powder in aqueous ammonia.Films were prepared from this type of precursor solution by spin-coatingand other coating or printing methods. In the prior art, the resultingZnO films have been applied to the fabrication thin-film transistors,wherein the substrate for deposition is typically SiO₂ or glass. TheseZnO films are polycrystalline or amorphous in nature, not epitaxial. AZnO film deposited by this method forms an entire ZnO layer, and doesnot serve as a seed or nucleation layer for subsequent solutiondeposition.

SUMMARY OF THE INVENTION

According to various embodiments of the present invention, provided is asolution deposition method for forming a metal oxide or metal hydroxidenucleation layer.

Additional features of the invention will be set forth in thedescription which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention.

An exemplary embodiment of the present invention provides a solutiondeposition method including: applying a liquid precursor solution to asubstrate, the precursor solution comprising an oxide of a first metal,a hydroxide of the first metal, or a combination thereof, dissolved inan aqueous ammonia solution; evaporating the precursor solution todirectly form a solid seed layer on the substrate, the seed layercomprising an oxide of the first metal, a hydroxide of the first metal,or a combination thereof, the seed layer being substantially free oforganic compounds; and growing a bulk layer on the substrate, using theseed layer as a growth site or a nucleation site.

An exemplary embodiment of the present invention provides a solutiondeposition method including: applying a liquid precursor solution to asubstrate, the precursor solution comprising an oxide of a first metal,a hydroxide of the first metal, or a combination thereof, dissolved inan aqueous ammonia solution; evaporating the precursor solution todirectly form a solid seed layer on the substrate, the seed layercomprising an oxide of the first metal, a hydroxide of the first metal,or a combination thereof, the seed layer being substantially free oforganic compounds; and growing a bulk layer a on the substrate, usingthe seed layer as a nucleation site, the bulk layer comprising an oxideof a second metal, a hydroxide of the second metal, or a combinationthereof, the second metal being different from the first metal.

An exemplary embodiment of the present invention provides a methodincluding applying a liquid precursor solution to a substrate, theprecursor solution comprising an oxide of a first metal, a hydroxide ofthe first metal, or a combination thereof, dissolved in an aqueousammonia solution; evaporating the precursor solution to directly form asolid seed layer on the substrate, the seed layer comprising an oxide ofthe first metal, a hydroxide of the first metal, or a combinationthereof, the seed layer being substantially free of organic compounds;and growing a bulk layer on the substrate, using the seed layer as agrowth site, the bulk layer comprising an oxide of the first metal, ahydroxide of the first metal, or a combination thereof.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention, andtogether with the description serve to explain the principles of theinvention.

FIG. 1 illustrates block diagram illustrating a solution depositionmethod according to various embodiments of the present disclosure.

FIGS. 2-4 illustrate structures formed during the method of FIG. 1.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

The invention is described more fully hereinafter with reference to theaccompanying drawings, in which embodiments of the invention are shown.This invention may, however, be embodied in many different forms andshould not be construed as limited to the embodiments set forth herein.Rather, these embodiments are provided so that this disclosure isthorough, and will fully convey the scope of the invention to thoseskilled in the art. In the drawings, the size and relative sizes oflayers and regions may be exaggerated for clarity. For clarity, likenumerals refer to like components.

The present disclosure pertains to the use of the method describedherein to produce a thin metal oxide or hydroxide film on a substrate.The film may be a seed layer for the growth of a bulk metal oxide ormetal hydroxide material layer, including the growth of a metal oxide ormetal hydroxide bulk layer using a solution based method.

Herein, a “growth site” refers to a structure composed, at least inpart, of a crystalline phase upon which crystal growth of that samephase occurs. For example, a “growth site” may operate as a seed forcrystal growth. In addition, a “nucleation site” refers to a structureupon which a crystalline phase may nucleate and grow, but is notcomposed of the same crystalline phase as the material that nucleatesand grows.

FIG. 1 is a block diagram illustrating a solution deposition methodaccording to various embodiments of the present disclosure. FIGS. 2-4illustrate structures formed during operations of the method. As shownin FIGS. 1 and 2, in operation 10, a precursor solution is applied to asubstrate 200 to form a liquid film 202. The precursor solution may beapplied using a method such as spin-coating, dip-coating, slot and diecoating, spray-coating, roll coating, transfer stamping or printing,inkjet printing, etc. The precursor solution may be applied at roomtemperature.

Operation 10 may further include preparing the surface of the substrate100 prior to the forming of the film 202. The surface may be prepared bywashing, or another surface preparation method designed to remove anysurface contamination, to create desired surface termination, orotherwise produce a surface conducive to film deposition.

The precursor solution may be formed dissolving a first compound in anaqueous solution including ammonia, such as 25-30 wt % NH₃ in H₂O. Thefirst compound may include a metal oxide and/or a metal hydroxide. Forexample, the first compound may be selected from ZnO, Zn(OH)₂, NiO,Ni(OH)₂, CuO, and Cu(OH)₂.

When the first compound includes a zinc compound, the resulting solutionmay contain water and the resulting soluble species of Zn(II) andammonia. The dominant soluble Zn(II) species include hydroxide andammine complexes of the respective forms, Zn(OH)_(x) ^(2-x) andZn(NH₃)_(x) ²⁺, where x is an integer between 1 and 4. The amount ofdissolved zinc can range from almost nothing up to the saturation limitin the solution, by controlling the amount of zinc oxide or zinchydroxide powder dissolved.

For a precursor solution saturated with dissolved zinc oxide or zinchydroxide, the precursor solution may be prepared, for example, byallowing an excess of zinc oxide or zinc hydroxide powder to equilibratewith an aqueous ammonia solution, and then separating the saturatedaqueous ammonia solution from any undissolved zinc oxide or zinchydroxide. The equilibration process may be accelerated by agitating theaqueous ammonia and zinc oxide or zinc hydroxide mixture, for example,by stirring, mixing, or shaking. The saturated aqueous ammonia solutionmay be separated from undissolved zinc oxide or zinc hydroxide powder byfiltration, for example, by filtering the mixture through one or moreporous membranes with pores small enough to prevent the passage of thezinc oxide or zinc hydroxide particles. The amount of zinc oxide powderdissolved in aqueous ammonia solution at saturation can be controlled bythe composition of the aqueous ammonia solution, for example, theammonia concentration of the solution, or controlled by the conditionsunder which the solution is saturated, for example, the temperature ofthe solution during saturation.

According to some embodiments, the precursor solution may include one ormore additional solvents or additives that do not substantially reactwith the dissolved metal species and evaporate from the liquid precursorfilm, as described below, so as to not remain in significant quantitiesin the solid seed layer that is formed. For example, the solution mayinclude common water miscible organic solvents including methanol,ethanol, isopropanol, n-propanol, and acetone.

According to some embodiments, the precursor solution may includeadditional dissolved elements, besides those of water, ammonia, and apure metal oxide or metal hydroxide, which do not evaporate from theliquid precursor film, as described below, and are incorporated into thesolid seed layer that is formed. The additional dissolved elements mayinclude elements which act as dopants or alloy the composition of theseed layer metal oxide or metal hydroxide compound. For a zinc oxideseed layer, for example, the additional elements may include Li, Na, Be,Mg, Ti, Zr, Hf, Cr, Mo, W, Mn, Fe, Co, Ni, Cu, Cd, Al, Ga, In, Si, Ge,Sn, P, As, S, Se, and F.

As shown in FIGS. 1 and 3, once the liquid film 202 is formed, thevolatile ammonia and H₂O, as well as any other volatile solvents oradditives present in the liquid film 202, are actively or passivelyevaporated, leaving a solid seed layer 204 behind. The evaporation mayoccur at a liquid film temperature ranging from the freezing and boilingpoints of the liquid film. For example, according to some embodimentswherein the precursor solution is primarily composed of ammonia and H₂O,the liquid film may be evaporated at a temperature ranging from −75° C.to 100° C. This may be achieved, for example, by holding the ambientenvironment temperature, the substrate temperature, or both, at atemperature in this range. In some embodiments, the liquid film may beevaporated at a temperature near room temperature, e.g., ranging from15° C. to 30° C., with or without any specific measures to control thistemperature. Following the evaporation, the seed layer 204 may be freeof organic compounds, or the seed layer 204 may be substantially free oforganic compounds, i.e., the seed layer 204 may contain no more than atrace amount of organic compounds. In other words, the evaporationdirectly results in the formation of the inorganic seed layer 204, whichdoes not include more than a trace amount of organic compounds.Therefore, a subsequent annealing process to remove such organiccompounds from the seed layer 204 may be omitted. As a result,processing time, process complexity, and thermal damage to substrates,may be reduced, as compared with methods for forming inorganic seedlayers wherein a solid precursor film containing organic compounds isfirst deposited and then converted to a fully inorganic seed layer bydecomposing or otherwise removing the organic components. Herein,“organic compound” refers to any chemical compound containing a carbonatom bonded to another carbon or hydrogen atom.

The seed layer 204 may have a thickness of from about 2 nm to about 20nm. The seed layer 204 may completely cover a surface of the substrate200. In the alternative, the seed layer 204 may be patterned on thesubstrate 200, such that the seed layer covers only selected portions ofthe surface of the substrate. In this case, the seed layer may be usedto template a pattern in the subsequent growth of the bulk layer 206, asdescribed below, by promoting growth of the bulk layer only on theselected portions of the surface covered with seed layer.

When the first compound includes zinc oxide, the Wurtzite crystalstructure of zinc oxide may be the thermodynamically stable phase forthe residual solid, i.e., the seed layer 204. However, at thetemperature of the evaporation in operation 20, the resulting solid maybe kinetically limited from completely forming Wurtzite ZnO. When theseed layer 204 is not completely converted into the thermodynamicallystable phase, the seed layer 204 may include trapped water and/orammonia. The complete reactions to form ZnO from the soluble Zn(II)species may be exemplified by Reactions 1 and 2 below. However,intermediate phases such as Zn(OH)₂ may be formed in this process, andmay remain in the seed layer, if the reactions are not taken tocompletion.Zn(NH₃)_(x) ²⁺(aq)+2OH⁻(aq)→ZnO+H₂O+xNH₃  Reaction 1Zn(OH)_(x) ^(2-x)(aq)+(x−2)NH₄ ⁺→ZnO+(x−1)H₂O+(x−2)NH₃  Reaction 2

As the H₂O and NH₃ in the liquid film 202 evaporate, the reactions aredriven forward to produce solid ZnO of the seed layer 204.

It has been shown that ZnO can display retrograde solubility dependenceon temperature in aqueous ammonia solutions. As the water, ammonia, andany other volatile components evaporate from the liquid film 202, andReactions 1 and/or 2 progress, the remaining liquid may be cooled by thetransfer of latent heat to the produced vapor. This cooling may produceincreased solubility for ZnO in the remaining liquid. This maycounteract the concentrating effect from evaporation, especially nearthe liquid-vapor interface. This may encourage nucleation and growth ofZnO at the solid-liquid interface, instead of the liquid-vaporinterface, so that films grow from the substrate up, rather than by aprecipitation and consolidation process occurring in the liquid film. Bygrowing from the substrate up, it becomes possible for the ZnO to bedeposited epitaxially, when the substrate 200 is suitably latticematched.

Other metal oxides and metal hydroxides, for example the metal oxidesand hydroxides of Cu(II) and Ni(II), form ammine complexes similar tothose of ZnO and have similar solubility behavior. Accordingly, theprecursor solution may include such compounds to form seed layersincluding copper and nickel metal oxides or hydroxides.

As shown in FIG. 1, the seed layer 204 may be optionally processed inoperation 30, in order to dehydrate, crystallize, and/or recrystallizethe seed layer 204. The processing may produce a desired crystallinity,grain size, etc. The processing may change the electrical behavior ofthe interface between the seed layer 204 and the substrate 200. Forexample, the processing may convert an electrical contact between theseed layer 204 and the substrate 200 from a Schottky electrical contactto an Ohmic electrical contact. The processing of the seed layer 204 mayincrease the resistance of the seed layer 204 to dissolution during theformation of a bulk layer discussed below.

In some embodiments, the processing of the seed layer 204 in operation30 may include a thermal treatment. The thermal treatment may occur at ahigher temperature than that of the evaporation used to form the seedlayer 204. For example, a thermal treatment at a temperature higher thanthat at which the seed layer 204 was evaporated may be applied to theseed layer 204. For example, the seed layer 204 may be heated to atemperature ranging from 100° C. to 600° C. In some embodiments, such athermal treatment may further dehydrate the seed layer 204, convert zinchydroxide in the seed layer into zinc oxide, crystallize an amorphousseed layer, or recrystallize a seed layer to have crystals of adifferent phase, size, shape, or orientation. As a result of such athermal treatment there may be a change in the electrical behavior ofthe interface between the seed layer 204 and the substrate 200, orimproved resistance of the seed layer to dissolution during theformation of a bulk layer, for example.

In some embodiments, the material of the seed layer 204 may have acrystal structure that allows for epitaxy on the crystal structure ofthe substrate 200. Accordingly, operation 30 may include treating theseed layer 204 under conditions that cause the seed layer 204 tocrystalize or recrystallize with a preference for a specific crystallattice orientation with respect to a crystal lattice of the substrate.For example, a ZnO seed layer may be deposited on a substrate comprisinga single crystal or epitaxial layers of GaN, and/or other relatedmaterials having a Wurtzite crystal structure with similar latticeparameters. Following the evaporation of the water and ammonia inoperation 20, the seed layer 204 may be thermally treated at elevatedtemperature in order to, first, further dehydrate the film and convertzinc hydroxide into ZnO, and second, to crystallize, or recrystallize,the resulting ZnO, so that it has a higher degree of crystal latticeorientation with respect to that of an underlying substrate. In someembodiments, a deposited ZnO film is on the order of 10 nm thick. Thethin nature of the ZnO film allows for a low energy barrier for theatoms of the ZnO seed layer, to crystallize, or recrystallize, into alattice that is oriented with respect to a crystal lattice of thesubstrate. As a result of this low energy barrier, the temperaturerequired to crystallize or recrystallize the ZnO seed layer is less thanwould be required to crystallize or recrystallize a thicker layer.

As shown in FIGS. 1 and 4, in operation 40 a bulk layer 206 is depositedthereon. For purposes of illustration, FIG. 4 shows the seed layer 204and the bulk layer 206 as being distinct layers. However, according tosome embodiments, the seed layer 204 may be substantiallyindistinguishable from the bulk layer 206. The bulk layer 206 may beformed using a low-temperature deposition process, with the seed layer204 providing nucleation sites or growth sites for the growth of thebulk layer 206. The bulk layer 206 may be formed by a solutiondeposition process selected from hydrothermal growth, solvo-thermalgrowth, chemical bath deposition, electrochemical deposition,electroless deposition, or successive ionic layer adsorption andreaction deposition (SILAR), for example.

According to some embodiments, the bulk layer 206 may include the samecompound as the seed layer 204. For example, when the seed layer 204includes an oxide of a first metal, a hydroxide of the first metal, or acombination thereof, the bulk layer 206 may include the same compound orcompounds as the seed layer 204. For example, the seed layer 204 and thebulk layer 206 may include one or more of the same compounds selectedfrom ZnO, Zn(OH)₂, NiO, Ni(OH)₂, CuO, and Cu(OH)₂. In this case, theseed layer 204 acts as a growth site for the crystal growth of the bulklayer 206.

For example, the seed layer 204 may include ZnO, and the bulk layer 206may include additional ZnO deposited by a solution growth methodresulting in a single ZnO layer. The solution growth method may includedeposition by a reaction at the substrate 200 surface, involvingdissolved ions in a surrounding solution. For example, the solutiongrowth method may include chemical bath deposition (CBD), hydrothermaldeposition, solvo-thermal deposition, electrochemical deposition,electroless deposition, or SILAR.

The crystal or crystals of the seed layer 204 provide energeticallyfavorable sites for the deposition of ZnO from the bulk layer growthsolution, so that the seed crystal or crystals grow larger. Because ofthe thin nature of the ZnO seed layer 204, the seed layer may besusceptible to dissolution during the bulk layer growth process when asolution growth method is used. The conditions for the growth on theseed layer 204 should be set such that the seed layer 204 is notcompletely dissolved by the growth solution before deposition of thebulk layer 206 on the seed layer 204 can occur. However, partialdissolution of the seed layer 204 may be desired as a means ofcontrolling the crystal grain structure of the bulk layer 206.

According to some embodiments, the seed layer 204 and the bulk layer 206may include different compounds. For example, when the seed layer 204includes an oxide of a first metal, a hydroxide of the first metal, or acombination thereof, the bulk layer 206 may include an oxide of a secondmetal, a hydroxide of the second metal, or a combination thereof, withthe second metal being different from the first metal. For example, theseed layer 204 and the bulk layer 206 may include different compoundsselected from ZnO, Zn(OH)₂, NiO, Ni(OH)₂, CuO, and Cu(OH)₂. In thiscase, the seed layer 204 acts as a nucleation site for the growth of thebulk layer 206. However, the bulk layer 206 may be formed of any othersuitable compound.

In an exemplary embodiment, the substrate 200 may be a group III-Nitridesemiconductor based optoelectronic device wafer. The precursor solutionused may include 25-30% aqueous ammonia and dissolved ZnO and/or Zn(OH)₂powder, and no other intentionally incorporated components ofsignificant concentration. Operation 10 and Operation 20 may includeapplying a liquid film of the precursor solution of the surface of thesubstrate 200, via spin coating, and then evaporating the same underambient room temperature conditions. Operation 30 may include heatingthe seed layer at about 500° C. in a flowing N₂ atmosphere. In thisembodiment, the treatment of Operation 30 makes the seed layer 204 moreresistant to dissolution during the deposition of a bulk ZnO layer 206,via an aqueous solution growth method in Operation 40. The ZnO seedlayer 204 and bulk layer 206 formed have an epitaxial relationship withthe substrate 200 and together form a transparent contact layer for thegroup III-Nitride semiconductor based optoelectronic device. Otherprocessing steps may be included either prior to operation 10, orsubsequent to operation 40, in order to form a final optoelectronicdevice structure.

It will be apparent to those skilled in the art that variousmodifications and variation can be made in the present invention withoutdeparting from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A solution deposition method, comprising:applying a liquid precursor solution to a substrate, the precursorsolution comprising an oxide of a first metal, a hydroxide of the firstmetal, or a combination thereof, dissolved in an aqueous ammoniasolution; evaporating the liquid precursor solution to directly form asolid seed layer on the substrate, the seed layer comprising an oxide ofthe first metal, a hydroxide of the first metal, or a combinationthereof, the seed layer being substantially free of organic compounds;processing the seed layer by at least one of dehydrating, crystallizing,and recrystallizing the seed layer, and heating the seed layer at atemperature ranging from 100° C. to 600° C.; and growing a bulk layer onthe substrate, using the seed layer as a growth site or a nucleationsite.
 2. The method of claim 1, wherein the substrate is a groupIII-Nitride semiconductor based optoelectronic device wafer.
 3. Themethod of claim 1, wherein the precursor solution further comprising 25%to 30% aqueous ammonia, dissolved ZnO powder, or dissolved Zn(OH)₂powder.
 4. The method of claim 1, wherein the bulk layer comprises anoxide of a second metal, a hydroxide of the second metal, or acombination thereof, the second metal being different from the firstmetal.
 5. The method of claim 1, wherein: the evaporating of theprecursor solution occurs at a first temperature; and the processing ofthe seed layer comprises heating the seed layer to a second temperaturethat is greater than the first temperature.
 6. The method of claim 1further comprising applying a liquid film of the liquid precursorsolution, via spin coating, and evaporating the liquid film underambient room temperature conditions.
 7. The method of claim 1, whereinthe seed layer and bulk layer have an epitaxial relationship with thesubstrate, and the seed layer, bulk layer and the substrate togetherform a transparent contact layer for a group III-Nitride semiconductorbased optoelectronic device.
 8. A method of producing a wafer,comprising: applying a liquid precursor solution to a substrate, theprecursor solution comprising an oxide of a first metal, a hydroxide ofthe first metal, or a combination thereof, dissolved in an aqueousammonia solution; evaporating the liquid precursor solution to directlyform a solid seed layer on the substrate, the seed layer comprising anoxide of the first metal, a hydroxide of the first metal, or acombination thereof, the seed layer being substantially free of organiccompounds; applying a liquid film of the liquid precursor solution, viaspin coating, and evaporating the liquid film under ambient roomtemperature conditions; and growing a bulk layer on the substrate, usingthe seed layer as a growth site or a nucleation site.
 9. The method ofclaim 8, wherein the substrate is a group III-Nitride semiconductorbased optoelectronic device wafer.
 10. The method of claim 8, whereinthe precursor solution further comprising 25% to 30% aqueous ammonia anddissolved ZnO powder or dissolved Zn(OH)₂ powder.
 11. The method ofclaim 8, wherein the seed layer and the bulk layer include differentcompounds.
 12. The method of claim 8 further comprising processing theseed layer by at least one of dehydrating the seed layer, crystallizingthe seed layer, recrystallizing the seed layer.
 13. The method of claim12 further comprising heating the seed layer at a temperature rangingfrom 100° C. to 600° C.
 14. The method of claim 8, wherein the seedlayer and bulk layer have an epitaxial relationship with the substrate,and the seed layer, bulk layer, and the substrate together form atransparent contact layer for a group III-Nitride semiconductor basedoptoelectronic device.